The world is going to become richer and richer as developing economies play catch up over the coming years, according to Willem Buiter, chief economist at Citigroup.

"We expect strong growth in the world economy until 2050, with average real GDP growth rates of 4.6 percent per annum until 2030 and 3.8 percent per annum between 2030 and 2050," Buiter wrote in a market research.

"As a result, world GDP should rise in real PPP-adjusted terms from $72 trillion in 2010 to $380 trillion dollars in 2050," he wrote.

As the world watches oil prices rise sharply amid unrest in the Middle East, Buiter's analysis of the world's long-term prospects offer some hope that better times are ahead but if he is right power will shift from the West to the East very quickly.

"China should overtake the US to become the largest economy in the world by 2020, then be overtaken by India by 2050," he predicted.

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Growth will not be smooth, according to Buiter. "Expect booms and busts. Occasionally, there will be growth disasters, driven by poor policy, conflicts, or natural disasters. When it comes to that, don't believe that 'this time it's different'."

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However, there are some easy wins for poor countries with big, young populations, he said.